This invention relates to an improved aqueous acid copolymer latex reinforced coal tar emulsion composition, and more particularly to rubberized coal tar emulsion containing butadiene/styrene/acid copolymer latices especially useful for applying a tough durable sealing coat to asphalt pavement surfaces.
Aqueous coal tar emulsions have been known and used in the art as protective coatings for many years. The most common form of aqueous tar emulsions used are coal tar in an aqueous medium with an emulsifying or dispersing agent such as an organic soap or detergent and/or an inorganic colloid such as a particulate clay like bentonite. In this type of prior art treatment the materials are reduced in tar particle size to the discontinuous or emulsified phase to produce tar particles of an average range size of from about 3 to 10 microns. It is known that when an ordinary emulsified coal tar coating dries upon an asphalt substrate, the dried coating exhibits certain disadvantages such as being attacked by gasoline, jet fuel, and the like.
It has been found that solvent resistance and elasticity of coal tar emulsions might be improved by the incorporation of a synthetic latex into the emulsion. Such polymer containing coal tar emulsions have in most instances been unsatisfactory apparently for the reason that the ultimate composition comprised an emulsion of different types of particles, namely, coal tar and polymer, and as the composition dried, a loose junction between latex and coal tar resulted which was readily broken down upon ordinary weather conditions, temperature, light, and other chemical and physical film-attacking agents. Moreover, in some instances the resultant protective coating had a tendency to re-emulsify when it was subjected to detergent and water. This difference in particle size was taken into consideration in the U.S. Patents to Walaschek Nos. 3,897,380 and 3,835,117 in which the acrylonitrile/butadiene copolymer was maintained at an average particle size of between 400 and 1000 .ANG.ngstroms.
U.S. Patent to Kemp et al No. 3,027,342 discloses a rubberized coal tar emulsion which avoids the use of an emulsifying agent. A dry copolymer of acrylonitrile and butadiene is incorporated into a coal tar composition and is emulsified in an aqueous medium without the addition of an emulsifying agent by vigorous mechanical mixing in a colloid mill or the like.
The patent to Kemp U.S. Pat. No. 3,296,165 discloses a coal tar emulsion composition comprising an emulsion coating including an emulsified coal tar/clay mixture and a butyl rubber latex. That composition further includes an aluminum powder additive and is especially suited for roofing applications. The patent to Chang U.S. Pat. No. 3,497,371 discloses a coal tar emulsion including certain filler materials and a synthetic rubber latex. The emulsion composition further includes certain water-insoluble organic amines for the purpose of imparting superior water resistance to films cast of those coal tar emulsions.